{"id":"CVE-2026-23319","state":"PUBLISHED","title":"bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim\n\nThe root cause of this bug is that when 'bpf_link_put' reduces the\nrefcount of 'shim_link->link.link' to zero, the resource is considered\nreleased but may still be referenced via 'tr->progs_hlist' in\n'cgroup_shim_find'. The actual cleanup of 'tr->progs_hlist' in\n'bpf_shim_tramp_link_release' is deferred. During this window, another\nprocess can cause a use-after-free via 'bpf_trampoline_link_cgroup_shim'.\n\nBased on Martin KaFai Lau's suggestions, I have created a simple patch.\n\nTo fix this:\n   Add an atomic non-zero check in 'bpf_trampoline_link_cgroup_shim'.\n   Only increment the refcount if it is not already zero.\n\nTesting:\n   I verified the fix by adding a delay in\n   'bpf_shim_tramp_link_release' to make the bug easier to trigger:\n\nstatic void bpf_shim_tramp_link_release(struct bpf_link *link)\n{\n\t/* ... */\n\tif (!shim_link->trampoline)\n\t\treturn;\n\n+\tmsleep(100);\n\tWARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link,\n\t\tshim_link->trampoline, NULL));\n\tbpf_trampoline_put(shim_link->trampoline);\n}\n\nBefore the patch, running a PoC easily reproduced the crash(almost 100%)\nwith a call trace similar to KaiyanM's report.\nAfter the patch, the bug no longer occurs even after millions of\niterations.","publishedAt":"2026-03-25T10:27:13.678Z","updatedAt":"2026-10-15T01:14:02.294Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e","status":"affected","lessThan":"529e685e522b9d7fb379dbe6929dcdf520e34c8c","versionType":"git"},{"version":"69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e","status":"affected","lessThan":"9b02c5c4147f8af8ed783c8deb5df927a55c3951","versionType":"git"},{"version":"69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e","status":"affected","lessThan":"cfcfa0ca0212162aa472551266038e8fd6768cff","versionType":"git"},{"version":"69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e","status":"affected","lessThan":"3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2","versionType":"git"},{"version":"69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e","status":"affected","lessThan":"4e8a0005d633a4adc98e3b65d5080f93b90d356b","versionType":"git"},{"version":"69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e","status":"affected","lessThan":"56145d237385ca0e7ca9ff7b226aaf2eb8ef368b","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/trampoline.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.0","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.0","versionType":"semver"},{"version":"6.1.167","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.130","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.77","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.17","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.7","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/trampoline.c"]}],"references":["https://git.kernel.org/stable/c/529e685e522b9d7fb379dbe6929dcdf520e34c8c","https://git.kernel.org/stable/c/9b02c5c4147f8af8ed783c8deb5df927a55c3951","https://git.kernel.org/stable/c/cfcfa0ca0212162aa472551266038e8fd6768cff","https://git.kernel.org/stable/c/3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2","https://git.kernel.org/stable/c/4e8a0005d633a4adc98e3b65d5080f93b90d356b","https://git.kernel.org/stable/c/56145d237385ca0e7ca9ff7b226aaf2eb8ef368b","https://cert-portal.siemens.com/productcert/html/ssa-082556.html","https://cert-portal.siemens.com/productcert/html/ssa-019113.html","https://cert-portal.siemens.com/productcert/html/ssa-457936.html","https://cert-portal.siemens.com/productcert/html/ssa-784472.html"],"weaknesses":[],"ingestedAt":"2026-10-29T20:11:21.040Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/23xxx/CVE-2026-23319.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-23319","state":"PUBLISHED","datePublished":"2026-03-25T10:27:13.678Z","dateUpdated":"2026-10-15T01:14:02.294Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-01-13T15:37:45.995Z"},"containers":{"cna":{"title":"bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim\n\nThe root cause of this bug is that when 'bpf_link_put' reduces the\nrefcount of 'shim_link->link.link' to zero, the resource is considered\nreleased but may still be referenced via 'tr->progs_hlist' in\n'cgroup_shim_find'. The actual cleanup of 'tr->progs_hlist' in\n'bpf_shim_tramp_link_release' is deferred. During this window, another\nprocess can cause a use-after-free via 'bpf_trampoline_link_cgroup_shim'.\n\nBased on Martin KaFai Lau's suggestions, I have created a simple patch.\n\nTo fix this:\n   Add an atomic non-zero check in 'bpf_trampoline_link_cgroup_shim'.\n   Only increment the refcount if it is not already zero.\n\nTesting:\n   I verified the fix by adding a delay in\n   'bpf_shim_tramp_link_release' to make the bug easier to trigger:\n\nstatic void bpf_shim_tramp_link_release(struct bpf_link *link)\n{\n\t/* ... */\n\tif (!shim_link->trampoline)\n\t\treturn;\n\n+\tmsleep(100);\n\tWARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link,\n\t\tshim_link->trampoline, NULL));\n\tbpf_trampoline_put(shim_link->trampoline);\n}\n\nBefore the patch, running a PoC easily reproduced the crash(almost 100%)\nwith a call trace similar to KaiyanM's report.\nAfter the patch, the bug no longer occurs even after millions 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